457
FXUS02 KWBC 191833
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
232 PM EDT WED AUG 19 2009
VALID 12Z SAT AUG 22 2009 - 12Z WED AUG 26 2009
TELECONNECTIONS WITH A RETROGRADING AND STRENGTHENING POSITIVE
ANOMALY MOVING ACROSS NUNAVUT THIS PERIOD FAVORS TROUGHING ACROSS
EASTERN AND WESTERN CANADA...AS WELL AS IMPLYING THE PROGRESSION
OF A DEEP CYCLONE TO ITS SOUTH ACROSS SOUTHERN CANADA...WHICH THE
MODELS ADVERTISE. THE WARM CORE RIDGE ACROSS THE ROCKIES IS
EXPECTED TO PROGRESS ACROSS THE GREAT PLAINS WHICH INITIALLY
ALLOWS FOR A DEEP CYCLONE ACROSS THE GREAT LAKES/MIDWEST BEFORE
THE SYSTEM PROGRESSES EASTWARD AS THE RIDGE UPSTREAM PROGRESSES
AND FLATTENS. AS FOR DETAILS WITHIN THIS MEAN FLOW... A TROUGH
AND EMBEDDED CLOSED LOW NEAR THE PAC NW/BC COAST EARLY DAY 3
/SATURDAY MORNING/ SHOULD PROGRESS EASTWARD ACROSS SOUTHERN CANADA
AND EXTREME NORTHERN CONUS AND THEN BEGIN TO RELOAD THE EASTERN
TROF.
DIFFERENCES SEEN IN THE EARLIER GUIDANCE CONCERNING A SYSTEM
CROSSING SOUTHWESTERN AND SOUTHERN CANADA LATE IN THE PERIOD WERE
RESOLVED BY THE 12Z GUIDANCE...AND LOOK SIMILAR TO CONTINUITY SO
NO CHANGES WERE MADE HERE. DOWNSTREAM...A TROUGH INITIALLY OVER
THE EASTERN STATES SHOULD EVENTUALLY WEAKEN/LIFT OUT... POSSIBLY
LEAVING SOME WEAK ENERGY BEHIND OVER OR NEAR THE SOUTHEAST. THE
TROUGHING OVER THE MIDWEST/NORTHEAST SHOULD DEFLECT HURCN BILL
AWAY FROM THE EAST COAST. CONSULT TPC DISCUSSIONS/ADVISORIES FOR
LATEST INFO REGARDING THE EXPECTED TRACK OF BILL... WHOSE FORECAST
POSITIONS ARE BASED ON THE 15Z TPC ADVISORY. THE 00Z/06Z GFS
STRAY FASTER THAN CONSENSUS/00Z MULTI-MODEL ENSEMBLE GUIDANCE WITH
PARTS OF THE INITIAL EASTERN CONUS SYSTEM...BECOMING FLATTER THAN
MOST MODEL/ENSEMBLE MEAN GUIDANCE WITH FLOW ACROSS THE EASTERN
PORTION OF THE LOWER 48 DURING MUCH OF THE PERIOD...AND THE 00Z
GFS SHOWS A GREATER SEWD EXTENT OF THE NERN PAC TROF BY NEXT
WEDNESDAY MORNING.
SINCE THE 00Z MULTI-MODEL ENSEMBLE GUIDANCE MIRRORS THE 00Z
CANADIAN/00Z ECMWF FOR MUCH OF THE PERIOD...A COMPROMISE OF THOSE
PIECES OF GUIDANCE WAS USED INTO EARLY TUESDAY. THEREAFTER...THE
00Z ECMWF MEAN/00Z ECMWF WERE USED... WHICH HAS SOMEWHAT BETTER
DEFINITION OF THE SYSTEM CROSSING SRN CANADA MOST OF THE PERIOD
COMPARED TO THE 00Z GEFS MEAN... TO ALLOW FOR TYPICAL DETAIL
UNCERTAINTIES AT THAT TIME FRAME. THIS PATTERN APPEARS WET ACROSS
THE EAST COAST EARLY ON...AND THEN ACROSS THE GREAT BASIN AND
NORTHERN TIER OF THE COUNTRY FROM THIS WEEKEND INTO MID NEXT WEEK.
ROTH/RAUSCH
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page